The invention relates to a delivery device for segments of a web fed in a feed direction and composed of film, for example bags, especially in a separating-seam welding machine. Such a machine can have a rotatably driven rotor whose axis lies in the feed plane or parallel thereto and can be equipped with a plurality of contact regions extending radially with respect to the rotation axis, whereby in operation the web sections fed so as to follow one another are gripped, swung out of the feed plane and deposited one above the other at a deposition station. The respective contact region of the rotor can encompasses suction regions which serve to hold the web section on the contact region with an underpressure when the contact region of the rotor travels over a circular segment between a first and a second angular position.
Such a delivery device is known. It comprises a rotor with bar-shaped gripper arms which extend radially and form the respective contact regions. Each gripper arm of the rotor with a respective pressure communication opening sweeps across an opening delivering underpressure (suction) in a part which is stationary in operation, the suction supply opening extending over the aforedescribed circular segment. When the respective pressure communication opening sweeps across the suction supply opening, underpressure (subatmospheric pressure) is applied to the suction openings of the contact regions of the gripper arm.
Depending upon the surface characteristics of the web section to be picked up and delivered, it is desirable to maintain an underpressure at the suction region either for as long as possible and thus until the delivery station is just reached or only up to a certain point in time before reaching the delivery station. The smoother the surface of the web segment, the smaller is the friction with which the respective web segment rests against the contact region of the gripper arm and thus the longer should the underpressure remain applied to the respective gripper arm so that the smooth web section does not slip. The rougher the surface of the material web the higher is the friction and thus the better is the adhesion of the material web of the contact region of the gripper arm. As a consequence it is advantageous in these cases to remove the suction from the suction region even before the delivery station is reached so as to prevent the plastic bag for example, which must be deposited on two spike-like projections, from tearing in the region of the spike-like projections because of excessive adhesion or even from separating at weakening lines which may be provided.
After an interruption in operation and thus the bringing of the manufacturing process for the web sections to standstill, a stationary part of the conventional apparatus which has an opening supplying the suction and extending in the peripheral direction, may be rotated which can cause the suction region of a gripper arm in the respective circular segment to be subjected to suction prematurely or too late. In the case of a premature elimination of the underpressure, in the first rotation the underpressure may be applied before the gripper arm comes into contact with the web section. This means that the suction region of the gripper arm is already subjected to underpressure at a point in time in which it has not yet come into contact with a web section to be picked up and to be swung away. The volume rate of flow of air in the rotor is then excessive and results in a reduction of the suction within the rotor. Web sections tend to adhere less well to the contact region of the gripper arm. Problems result because there is an insufficient resistance to the air flow by the web sections in the operation of the device. The web sections can slip on the contact regions of the gripper arm and the operation of the delivery device is defective. The down time of the machine which is provided with the delivery device increases.
The object of the present invention is to improve a delivery device of the type described at the outset so that suction control is possible during the delivery of the web section and simultaneously the danger which arises in operation of the machine is not increased, i.e. a reliable securing of the web section to the contact region of the rotor is ensured.
This object is achieved with a delivery device of the type mentioned according to the invention in that the angle of the circular segment, within which the suction region of the contact region is subject to suction pressure is adjustable within limits.
In the delivery device of the invention it is also possible after adjustment or adjustable setting of the first angular position, preferably such that suction is applied to the suction region exactly at the point in time in which the contact region comes into contact with the web section, the second angular position can be adjusted corresponding to the surface characteristics of the web section. Thus according to the invention there is not a fixed circular segment angle which can be rotated as such in the rotation direction or counter to the rotation direction, but a variation in the size of the circular segment and thus the size or the circumferential length of this region over which suction remains applied to the suction region. It has been found to be advantageous and satisfactory when the first angular position is not adjustable and the second angular position is provided so as to be adjustable. In this manner, the first angular position can be set so that the time point of underpressure application coincides with the time point at which the contact region of the rotor contacts the web section. The disadvantage of the known device, that too great a volume flow takes place via the suction region into the interior of the rotor and the underpressure remaining there drops, can be avoided.
According to the present invention, respective separately controllable spaces can follow one another for example in the rotation direction and in which respective underpressures are generated and can be swept by the respective pressure communication openings of respective contact regions of the rotor. The size and therefore the angle of the circular segment in which an underpressure application to the suction region of the rotor arises can be achieved by a corresponding adjustment or nonadjustment of the openings.
A preferred embodiment of the invention is characterized in that a mouth opening of a passage connected to the suction region of a respective contact region and rotating with the contact region is provided in the region within the circular segments with one or more openings extending in the rotation direction or arranged in the rotation direction and communicating with the contact regions while between the mouth opening of the passage and the suction supplying opening at least one control element defining a control opening is provided which is rotatable relative to the rotor. According to this inventive concept, the size of the angle and thus the angular extent or length of the circular segment within which there is application of suction to the respective suction region is varied by the setting element and such that at least one control opening in the setting element extends or shortens the suction feed opening in the circumferential direction.
From a point of view of manufacture, it has been found to be advantageous for the underpressure feed opening to be formed by a part which is stationary relative to a machine frame in operation. In this manner it is possible to exactly define the first angular position relative to the feed plane of the material web sections. Furthermore, any optional passage means, which need not be flexible can be used for pressure communication between the underpressure feed opening and device for generating the underpressure.
The aforementioned stationary part can form a hub through which a drive train for the rotor can extend.
According to a further preferred embodiment, the stationary part, especially the hub, bounds the compartment feeding the suction and extending in the peripheral direction and which opens via the suction supply opening in a sealing surface against which the setting element lies slidingly with its control opening. The suction supply chamber provides a sufficient suction capacity. As a consequence of the fact that the suction supply chamber is formed directly in the stationary part, it is possible without further passage means between them to have the suction chamber open directly via the suction supply opening in the sealing surface so that the greatest possible flow cross section is available and such that only the size of the mouth opening of the respective duct means of the contact region is limiting.
While the sealing surface does not necessarily have to be planar to be useful (it can also have a cone shape), it has been found to be advantageous for the setting element to be disk-shaped or flange-shaped and to be rotatable relative to the suction supply opening about the rotation axis. The system thus does not deal with a linearly shiftable slide or shifting element but rather the setting element is rotatable about the same axis is as the rotor with respect to which the suction supply opening is bounded.
The setting element is, in a further feature of the invention, advantageously rotatably limited by a stop element. In an especially advantageous further feature of this inventive concept, the stop element is formed by a projection projecting over the sealing surface into a recess of the setting element.
According to still a further inventive concept, the projection bounds the suction supply opening on one side in the peripheral direction and engages as sealing cams in a control opening of the setting element. The projection serves thus at the same time as a stop element and as the means defining the first angular position independently of the instantaneous setting of the setting element.
When the delivery device is to reliably release the web section from the contact region following the underpressure application to the contact region, an overpressure application to the contact region should be effective and thus it is especially advantageous for there to be an overpressure energized section following the control opening of the setting element in the direction of rotation of the rotor which is swept over in operation by the mouth opening of the duct means. The invention in a further feature proposes that the section to which overpressure is applied be formed within the setting element. It can, in this case, be formed by a radial and axial opening communicating a compressed air connection.
It has been found to be advantageous further for the setting element to be rotatably driven with respect to the underpressure feed opening by a motor, which can be pneumatic or hydraulic, or driven in some other way. For this purpose, the setting element can have on its outer periphery coupling means, for example in the form of teeth, an articulation for a reciprocating rod or the like. It is however also possible to provide internal teeth on an appropriate section of the setting element which can mesh with a pinion as long as that section is radially outwardly of the drive train for the rotor.